1. Field of the Invention
The present invention relates to a rotation sensor, such as a steering sensor for an automobile, which is capable of measuring the angle of rotation of a shaft and torque acting thereon.
2. Description of the Related Art
With the recent movement toward the conservation of global environment, researches have been devoted to reducing the weight of a vehicle body, as a measure to reduce the exhaust gas from the automobile. One of such measures for lightening the vehicle body is to replace a hydraulic power steering assembly, which is one of the causes of increased weight of the vehicle body, with an electric power steering assembly. However, in the case of using an electric power steering assembly, an assisting force for a steering shaft needs to be computed using a computer. Accordingly, the electric power steering assembly requires two sensors, i.e. a rotation angle sensor (steering angle sensor) for measuring the rotational angle (steering angle) of the steering shaft and a torque sensor for measuring the torque applied to rotate the steering shaft. Thus, the number of components increases, making it difficult to reduce the weight of the vehicle body as intended.
Such a rotation angle sensor or torque sensor conventionally includes a type having mechanism where a brush is disposed in sliding contact with a conductive ring arranged concentrically with the shaft, for detecting the rotation angle or torque of the shaft. The mechanism, however, has a disadvantage that metal powder scatters due to friction when the brush and the slip ring, both made of metal, are in siding contact with each other. The metal powder undergoes a mechanochemical reaction with organic gas in the air, causing the formation of an insulating film and consequent unexpected increase of electric resistance.
It is possible to avert such increase of electric resistance by increasing the contact pressure of the brush and thereby scraping away the insulating film. However, this shortens the life duration of the slip ring.
It is an object of the present invention to provide a rotation sensor which functions as both a rotation angle sensor and a torque sensor and is capable of overcoming the aforementioned shortcomings.
It is another object of the present invention to provide a rotation sensor which ensures a long life duration of a slip ring.
According to the present invention, to accomplish the aforementioned objects there is provided a rotation sensor comprising an active rotor, a follower rotor arranged adjacent to the active rotor, the follower rotor sharing a rotation axis with the active rotor and capable of rotation following the active rotor, and a casing containing the active and follower rotors and allowing the rotors to rotate freely, wherein a disk-like slip-ring retainer plate is secured to an outer periphery of the active rotor for rotation together therewith, a pair of feeder slip rings, a pair of rotation-angle measuring slip rings, and a pair of torque measuring slip rings are all disposed on the slip-ring retainer plate and concentrically with the active rotor, the rotation-angle measuring slip rings and the torque measuring slip rings are covered with conductive resin, the torque measuring slip rings are arranged on one side of the slip-ring retainer plate facing the follower rotor, the feeder slip rings and the rotation-angle measuring slip rings are arranged on the other side of the slip-ring retainer plate opposite to the torque measuring slip rings, feeder brushes and rotation-angle measuring brushes are fixed to the casing for sliding contact with the feeder slip rings and the rotation-angle measuring slip rings, respectively, a disk-like torque measuring brush retainer plate is connected to an outer periphery of the follower rotor for rotation together therewith, torque measuring brushes are fixed to the torque measuring brush retainer plate for sliding contact with the respective torque measuring slip rings, the feeder bushes are electrically connected to each other and are connected to a power supply device, the rotation-angle measuring brushes are electrically connected to the feeder brushes and a rotation-angle computing device, and the torque measuring brushes are electrically connected to the feeder brushes and a torque computing device.
Other objects, features and advantages of the present invention will be apparent from the following detailed description.